Practical transmission of signals by optical beams through thin transparent fibers rather than by electrical currents through electrically conductive wires or radio waves became a reality after the development in the early 1960's of the laser which provides a stable source of coherent light. The emergence of the concept of "integrated optics", wherein wires and radio links were replaced by optical fibers rather than through-the-air optical paths progressed further by development of miniaturized optical integrated circuits to replace conventional circuits. This major advance was enhanced by the creation of gallium aluminum arsenide (GaAlAs) diodes and photolithographic microfabrication technology capable of production ultraminiature devices with submicron line widths.
Advantages of the current state of optical fiber transmission lines over electrical counterparts include its stability, its wide bandwidth, its freedom from noise and external interference and its greater utility afforded by the small size of practical equipment. The last advantage is obtained by using miniature semiconductor lasers for introducing optical signals into an optical fiber and coupling photodiodes to the fiber for detection. Earlier systems, however, required bulky, vibration-sensitive combinations of mirrors, prisms, and gratings to direct an optical beam carrying a signal from the emitter (laser) to the appropriate photodiode detector. Although such apparatus was at least comparable to or better in the reliability than existing electrical means of signal transmisson, this and other difficulties have retarded acceptance of fiber-optic signal transmission.
One of the difficulties of earlier systems was the necessity for separate emitter and detector diodes to introduce the signal at one end of a fiber and to detect of the signal at the other end of the fiber. This difficulty was significantly mitigated by Hunsperger in a system (U.S. Pat. No. 3,952,265, issued Apr. 20, 1976, to R. G. Hunsperger) which provides a unitary dual mode diode which can function as an emitter or detector. Basically, this dual mode diode is a p-n junction diode that functions as a laser when forward biased and as a photodiode when reverse biased, or with no voltage applied, the diode is in a neutral state with a relatively low insertion loss which does not interfere with the functioning of other devices on the transmission line.
The present invention recognized the severity of the problem of vibration sensitivity in coupling diodes to optical fibers and other waveguides, limiting the quality of transmission and performance of equipment. Further, mechanical instability of systems of mirrors, prisms, and gratings made installation in certain field applications, such as aircraft, awkward.
Accordingly, it is an object of the invention to provide diode devices for introducing optical signals into a fiber-optic line or other waveguide and receiving optical signals from fiber-optic lines or other waveguides, the device being substantially free of adjuncts with high sensitivity to mechanical disturbances and vibration.
It is another object of the invention to provide a p-n junction diode for direct coupling to a fiber-optic transmission line.
It is still another object of the invention to provide a unitary device capable of functioning as an emitter for introducing an optical signal into a fiber-optic transmission line and receiving an optical signal from a fiber-optic transmission line or other waveguide to which it can be coupled directly.
These and other objects will be apparent from the specification with accompanying drawings and claims.